var stream = require('stream');
var Readable = stream.Readable;
var ch = 'a'.charCodeAt(0);
function MyReadable(){
    Readable.call(this);
    this._read=() =>{
        if (ch<='z'.charCodeAt(0)) {
            this.push(String.fromCharCode(ch++));
        }else{
            this.push(null)
        }
        
    }
    
    this.pipe(process.stdout);
}
MyReadable.prototype=Readable.prototype;
var obj = new MyReadable();